This invention relates to an arrangement for an improved seal assembly.
During assembly of a shaft and seal assembly comprising a contacting circumferentially segmented carbon seal, the complimentary sealing surfaces of the carbon seal and shaft are often damaged. As disclosed in U.S. Pat. Nos. 4,082,296 and 5,558,341 circumferentially segmented seals are sprung loaded against the housing so as to apply a radially inwardly pressure against the shaft. Conventionally during assembly a tool is inserted radially inward of the segmented seal, which is so arranged to then radially dilate the seal allowing the shaft to be inserted. The tool is then withdrawn in an axial direction.
In operation the housing is filled with a pressurised mixture of air and oil while higher pressure air is present outside the housing. The seal controls the amount of air entering the housing, between the rotating shaft and the seal ring, and also prevents oil escaping, from the housing, to the region outside the housing. The prevention of migration of a pressurised fluid across the seal may be optimised by providing the least possible clearance between the seal and the shaft surface. Although this type of seal is effectively a contact seal, a film of oil typically 1-3 molecules thick is preferably provided for lubrication between the seal and the shaft. It is essential therefore that the complimentary surfaces of the seal and shaft are not damaged in any way during assembly. It has been found that insertion and removal of the tool causes both axial scoring of the complimentary surfaces and chipping of the carbon seal. This axial scoring results in a significant reduction in the effectiveness of the seal.
It is the object of the present invention to provide apparatus to prevent the segmented seal and the shaft being damaged during assembly of the shaft to the seal housing.
According to the present invention a seal assembly for co-operation with a shaft comprising a sealing member which, in use, in a first position, forms a seal against the shaft, a seal housing for retaining the seal member, means for applying a radially inward force to the seal member and means for applying a radially outward force to the seal member so that, when the means for applying a radially outwards force is operated, the seal member is dilated to a second position thereby enabling the seal assembly and the shaft to be fitted and disassembled in conventional manner, when the means for applying a radially outward force is removed the means for applying a radially inward force to the seal member returns the seal member to the first position.
Preferably the seal assembly is a substantially circumferential seal assembly and the seal member is a substantially circumferential seal assembly. Alternatively, the seal assembly is a substantially axial seal assembly and the seal member is a substantially axial seal member.
Preferably, the means for applying a radially inward force to the seal member comprise a resilient member, the resilient member disposed between the seal housing and the seal member. Preferably, the resilient member is a garter spring.
Preferably, the seal member comprises a magnetic material. Alternatively, a magnetic material is disposed to the seal member.
Preferably, the garter spring is attached to the sealing member. Preferably, the garter spring comprises a magnetic material. Alternatively, the garter spring comprises a magnetostrictive material. Alternatively, the garter spring comprises an electrostrictive material.
Preferably, the means for applying a radially outward force to the seal member comprises a collar comprising magnetic coils which is so disposed to the magnetic material that, in use, the seal member is dilated to a second position. Alternatively, the means for applying a radially outward force to the seal member comprises a collar comprising a permanent magnet which is so disposed to the magnetic material that, in use, the seal member is dilated to a second position. Alternatively, the means for applying a radially outward force to the seal member comprises subjecting the garter spring to an electric current thereby dilating the garter spring and the seal member to the second position.
Alternatively, the means for applying a radially outward force to the seal ring comprises a tube which is so disposed to the seal ring that, in use, when the tube is internally pressurised the seal ring is dilated to a second position. Preferably, the tube is an elastomeric material. Preferably, the tube is disposed within the garter spring.
Preferably, the seal member comprises any material selected from the group of carbon, diamond-like carbon, fluoropolymers, polytetrafluoroethylene.
Preferably, a back plate and retaining ring are disposed in operative association with the seal housing to support a second resilient member, the second resilient member providing a substantially axial force to axially position the seal member in the seal housing. Alternatively, the seal housing comprises an integral back plate and retaining ring.
Preferably the second resilient member is a spring.